1. Field of the Invention
The present invention relates to ultrasonic processing of laminates. In particular, the present invention relates to an apparatus and method for ultrasonic debulking or welding of laminates.
2. Description of Related Art
Laminate materials are widely used in many industries, such as the aerospace industry. Laminate materials include polymeric composite laminates, such as thermoplastic and thermosetting composite laminate materials, and metallic laminates. Many applications of such thermosetting composite materials are structural in nature, wherein the quality of the material is a critical factor. For example, it is desirable to eliminate air entrapped within uncured composite laminates prior to curing or consolidation.
Generally, manufacturing polymeric composite materials involves impregnating a polymeric resin into a volume surrounding a plurality of fibers, forming a layer or ply of fibers disposed in a matrix of resin. Often the impregnation process is accomplished prior to assembling or “laying up” a plurality of layers or plies into an assembly or “layup”, which is subsequently heated or “cured” to form a product.
The impregnation process is critical in controlling air entrapped in a layup and the uncured thickness of impregnated material. An incomplete impregnation often results in air entrapment inside the composite material. Air can also be trapped between layers or plies of composite material during the layup process. Such trapped air causes the volume of an uncured part to be greater than that of a cured part. The volume of air entrapped in a part is known as “bulk.” Excessive bulk often causes “marcels” and/or voids in cured composite parts. Marcels are fibers that become wavy during handling and/or curing because the fibers are pushed by excessive, unbalanced forces of the manufacturing process.
Bulk compaction or “debulking” at room temperature or with heat and under vacuum is a conventional practice used during part layup to curb bulk-induced quality anomalies. Conventionally, a debulking cycle includes touch labor associated with vacuum bagging the part, heating the part to and cooling the part from a debulking temperature, and unbagging the part. Such debulking cycles may require up to eight or more hours to complete. Moreover, the debulking temperature must be carefully selected so that the composite material is not significantly advanced or staged during the debulking process. Thicker composite parts often require multiple debulking cycles, which contribute significantly to the total part cycle time and cost.
One way of decreasing the amount of time to debulk a composite layup is to apply ultrasonic vibration to the layup. In this approach, an ultrasonic horn is engaged with a top surface of a stack of polymeric composite material layers or plies. The ultrasonic horn is energized to induce cyclical deformation in the plies to heat the plies, reduce the resin's viscosity, and enhance wetting of the fibers with resin. The vibrating horn is moved along the upper surface of the stack to consolidate the layers or plies. Moreover, the ultrasonic vibration helps entrapped gases to coalesce and form larger bubbles, which can be more easily pushed out under the “sweeping” motion of the vibrating ultrasonic horn. However, conventional ultrasonic debulking techniques may induce excessive heating of the composite material stack. Such excessive heating often results in inadvertent substantial cross-linking (i.e., curing) of thermosetting resin components. Moreover, such excessive heating may cause degradation of the resin and/or the polymeric composite material. Such deficiencies may cause degradation of the cured thermosetting composite part, resulting in reduced mechanical properties of the part.
Layers or plies of laminate materials may be ultrasonically welded to adjacent layers or plies. In such laminates, most designs require adjacent layers or plies to be welded across the entire adjacent surfaces. Conventional ultrasonic welding processes, however, do not compensate for in-process variations that may result in welded laminates that exhibit substandard quality.
While there are many procedures for ultrasonically processing laminate materials that are well known in the art, considerable room for improvement remains.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.